Isometric isoindoline yellow pigment

Abstract

Pigment of formula wherein R1 is CONR4R5 or C(═NR6)NR7R8, R2, R3, R4 and R5 are each independently of the others H, C1-C5alkyl, or phenyl which is unsubstituted or substituted from 1 to 5 times by C1-C5alkyl or by halogen, R6 is phenyl which is unsubstituted or substituted from 1 to 4 times by C1-C5alkyl or by halogen, R7 is H or C1-C5alkyl, and R8 is a direct bond or a carbonyl bridge to R6, which pigment consists of primary particles the average aspect ratio of which is from 4 to 1, preferably from 3.5 to 1, especially from 3 to 1, and for the ellipses equivalent to the contours of the primary particles on a two-dimensional electron microscopic image have an average numerical eccentricity ε of from 0 to 0.80, the numerical eccentricity ε being defined as (formula), wherein a is the semimajor axis and b is the semiminor axis of the equivalent ellipse. That pigment preferably has a narrow particle size distribution and is, as are analogous pigments, prepared by a novel process. The invention relates also to a process for the preparation of that pigment, wherein R1CH2CN or (formula) is dispersed in an acidic aqueous medium containing from 70 to 99% by weight water, preferably in the presence of a dispersant, and is reacted with solid (formula). preferably ɛ = a 2 - b 2 a

Dependencies are inferred from the claim text.